DESCRIPTION (OVERALL) (provided by applicant): This Program Project represents a coordinated and mutually supporting effort to pursue research in structural biology where electron diffraction and electron microscopy play a key role and to advance the technology that enables this research. Three projects within the Program represent applications of the methods of electron crystallography and microscopy, as well as of the instrumentation supported by the Program, to specific problems in structural biology. These applications include: Studies of the structure of tubulin and its interactions with ligands and other proteins that affect the dynamics of the microtubule cytoskeleton; Studies on condensins, proteins responsible for condensation of chromatin; Studies of the conformational changes that follow nucleotide hydrolysis in tubulin or that occur upon binding of drugs that inhibit polymerization. Additional, separately funded research projects which rely on equipment and facilities supported by the Program Project are also included as Associate member projects. The Administrative Core maintains the major equipment, supports computer resources, and provides a sense of intellectual community and common identity for all the participants in the Program Project.